Cracking and Alkenes

• Thermal decomposition reaction - breaking down molecules by heating.
• Catalytic cracking

  1. Heat long chain hydrocarbons and vaporise.
  2. Hot powdered aluminium oxide.
  3. Pass hydrocarbon vapour over powder.
  4. Split apart into 2 smaller hydrocarbons as they come into contact with the catalyst.
• Steam Cracking

  1. Heat long chain hydrocarbons and vaporise.
  2. Mix with steam.
  3. Heat to a very high temperature.
  4. Long chains split apart.
• A cracked long chain alkane makes a shorter chain alkane + an alkene.
• There isn't enough hydrogens left for both products to be saturated and all have single bonds after cracking. This is why there is an alkene produced.

  
• Instead of the alkene being a waste product they are used to create polymers and are the starting materials for other chemicals.
• Alkenes are a part of the homologous series.
• The difference between alkanes and alkenes is that alkanes have single bonds whereas alkenes have double bonds.
• Alkenes are more reactive than alkanes.
• If bromine water is added to alkenes they will decolourise the bromine water from orange to colourless.
• Alkenes can be added together to make polymers.